This invention relates to one-way valves and especially to replacement valves for use within the human circulatory system.
The veins of the human circulatory system have one-way valves comprising two leaflets (known as bicuspid valves), which promote the flow of blood from the extremities back to the heart by preventing the retrograde flow of blood to the extremities between heart beats. The presence of the venous valves also allows muscular action to assist in the pumping of blood from the venous side of the circulatory system back to the heart. The contraction of various muscles tends to constrict the veins, forcing blood to flow, and the venous valves permit only one-way flow back to the heart.
The veins are subject to various disorders related to defective structure and function of their valves, known as valve incompetence. Valve incompetence can cause varicose veins, as well as chronic venous insufficiency wherein the valve leaflets become thickened and contracted so that they become incapable of preventing the retrograde flow of blood. Both of these conditions cause considerable discomfort and can lead to further complications such as edema, erythema, dermatitis, skin ulceration and cellulitis.
Tricuspid valves (having three leaflets) are found in the heart and enable the heart to act as a pump by allowing only one-way flow of blood. The heart valves are also subject to various disorders such as mitral stenosis, mitral regurgitation, aortic stenosis, aortic regurgitation, mitral valve prolapse and tricuspid stenosis. These disorders are serious, potentially life threatening and may be treated by surgical replacement of the affected valve.
Artificial endovascular valves for the replacement of incompetent venous valves or diseased heart valves should be bio-compatible, long-lasting, and have the appropriate hemodynamic characteristics which approximate those of natural valves to properly control and promote the flow of blood throughout the circulatory system. Such endovascular valves may also find use in artificial hearts and artificial heart assist pumps used in conjunction with heart transplants.
The invention concerns a one-way valve positionable within a lumen of a vessel, such as a vein. The valve according to the invention comprises a flexible tube formed of intermeshed filaments, which are preferably intermeshed by braiding. The tube has an upstream end and a downstream end which are oppositely disposed from each other. A radial support is attached to the tube at the upstream end. The radial support biases the tube radially outwardly into an open configuration which allows fluid within the vessel to flow relatively unimpeded into the valve from the upstream end. A plurality of flexible leaflets comprises the downstream end. The leaflets have surfaces facing inwardly of the tube. The leaflets are interengagable with each other and movable from a closed position wherein the surfaces are in sealing contact to stop flow through the valve in an upstream direction and an open position wherein the leaflets are separated apart from one another to permit fluid flow through the valve in a downstream direction. The leaflets are normally biased toward one another by a biasing means, allowing them to be readily moved into the closed position. Alternately, the leaflet may be biased into the closed position.
In one embodiment, the biasing means comprises the intermeshed filaments forming the tube themselves being resilient and biased by internal elastic forces into a converging shape wherein the surfaces of the leaflets are biased toward one another or in sealing contact. In the preferred embodiment, the biasing is provided by a resilient, flexible membrane covering the tube. The membrane has a converging shape which forces the surfaces of the leaflets toward each other or, alternately, into sealing contact. Preferably, the valve has two leaflets, although three leaflet valves are also feasible.
For higher pressure operations, it may be necessary to support the valve with one or more elongated supports arranged lengthwise along the tube. Preferably, the elongated supports are intermeshed with the filaments comprising the tube and prevent it from collapsing when subjected to pressure from the downstream end. The elongated supports may be integrally formed with the upstream radial support or may be connected between an upstream and a downstream radial support. Preferably, the radial supports push outwardly against the wall of the vessel to fix the valve in place. However, for relatively higher pressure applications fasteners having vessel engaging portions projecting outwardly from the tube may be used to fix the position of the valve by attaching it to the vessel wall.
It is an object of the invention to provide a one-way valve which can be implanted in a vessel of the human vascular system.
It is another object of the invention to provide a one-way valve which is compatible with human tissue.
It is yet another object of the invention to provide a one-way valve which is simple, inexpensive and long lasting.
It is still another object of the invention to provide a one-way valve which has hemodynamic characteristics similar to natural valves.
These and other objects of the invention will become apparent from a consideration of the following drawings and detailed description of the preferred embodiments.